The mysterious tragedy at the heart of Rothko's tranquil masterpieces

In May last year a picture by Mark Rothko was sold at Sotheby's, New York for $72.8 million, which was then the record price for a post-war work of art at auction.

It was an event that would almost certainly have appalled and infuriated the artist. He would, if anything, have been even more agitated by a new retrospective exhibition of his work at Tate Modern.

Rothko (1903-1970) is one of the great figures of mid-20th-century American art, his name often paired with that of Jackson Pollock. Pollock and Rothko have come to represent the pinnacle of post-war abstract art. But the two had little in common (except for heavy drinking, a common factor among most artists and writers of that era). Rothko rejected the label of"action painting", pointing out that his aim was more meditation than action.

Nor did he accept that he was a" colourist", despite the fact that his mature work consisted of nothing but large fussy patches of pigment. In an especially contrary moment, according to his friends Barbara Novak and Brian O'Doherty, Rothko even denied that what he produced was"art" - instead" communication on an exalted level of experience".

Indeed, looking at a Rothko can be a meditative, almost mystical affair. The more you look, the more you see subtle shifts and nuances of touch and hue. In his later work, such as the Rothko Chapel pictures, it takes some time before anything at all emerges from the gloom; then slowly you begin to discern a glimmer of slightly lighter darkness at the heart of the painting.